Comprehensive Description

Comprehensive Description

Mahonia aquifolium (synonym Berberis aquifolium) commonly known as Oregon grape or holly-leaf Oregon grape, is a broadleaf evergreen shrub of the barberry family (Berberidaceae).Mahonia aquifolium is native to western North America from British Columbia to California and eastward to Idaho and Montana. It was introduced horticulturally from the Pacific Northwest into Europe in 1822 and is considered an alien invasive species there, having been particularly successful in central and eastern Germany (CABI 2011). M. aquifolium is the state flower of Oregon.

Oregon grape produces pinnately compound leaves that are about 10” long, with each leaf having 5-9 spiny ovate or oblong-ovate leaflets around 3” long. The thick, glossy, deep green leaves are reminiscent of holly, are reddish bronze in new growth, and are purplish bronze in winter. This medium-sized shrub typically grows to about 3-6 feet in height, spreading from 2-5 feet (NPIN 2016). The bright yellow flowers are borne in dense clusters and are followed by dark blue-black berries in summer. The plant spreads by growing stolons to form colonies. Each small flower has 6 petals opposite 6 stamens, surrounded by 6 bright yellow sepals. At the base of the flower are 3 green/yellow bracts about half as long as the sepals (CABI 2011; Missouri Botanical Garden 2016).

M. aquifolium grows primarily in rocky woods and coniferous forests in the Northwest. Often the understory of Douglas fir stands. it prefers moist, organically rich, acidic, and well-drained soil in shady or partly-shady areas. Oregon Grape is a perennial angiosperm that flowers each year in January through May. The berries appear from late summer to early fall and remain on the plant through winter, while the seeds ripen from August through September. The life cycle of M. aquilifolium is dominated by the diploid sporophyte generation. While it mostly relies on pollinators for distribution of genetic material, it is also able to self-pollinate, and it can reproduce via root sprouts and stem layers (CABI 2011). It is of great value to native pollinating bees as it attracts them in large numbers, and it also serves as a food source for birds and other animals, which then help to disperse the seeds.